Mihail Teodorescu

The advantages, limitations and disadvantages of Z-source inverter

A Z-source converter is an unique x-shaped impedance network called Z-source impedance network that couples the converter main circuit to the power source. The converter may be of all conversion types - if it is of ac-to-dc type, the z-source converter is called z-source inverter. Since 2003 when this recently conversion concept appeared [1], it proved able to solve many conversion problems. In this paper its superiority compared to traditional solutions are shown. There are also small disadvantages and limitations revealed.

Single-phase active power filter with improved sliding mode control

This paper presents a study about a single-phase shunt active power filter with sliding mode control. The operation mode of the shunt active filter is detailed, introducing a new operating mode for the inverter in order to improve the behavior of the line current during the zero-passings. Regarding sliding mode control, the sliding surface, the existence condition and the equivalent control are analysed. The steady-state error is diminished by implementing a proposed sliding surface, which includes the current error and its integral. The expected results are confirmed through simulation.

Zero steady-state error PWM control system for sinusoidal voltage

The paper presents a PWM control system of a sinusoidal voltage using a single-phase inverter that comprises at the output a LC low-pass filter with resistive load. The PWM control strategy of a sinusoidal voltage and the optimization of the control loop via the modulus criterion, for step input signals, are presented. The steady-state error of the PWM control system is analyzed for sinusoidal input signal and methods for reducing the steady-state error by increasing the switching frequency and by adding an integral element series to the modulus criterion optimized controller are presented. If analyzed as a linear system, the addition of an integral element would make the system unstable, due to a double pole in the origin, but it is shown that by analyzing the system as a nonlinear system having an ideal relay-type nonlinearity, stability is preserved. Further, knowing that the steady-state error for sinusoidal input can be nullified by introducing a resonant element, a new utilization of a resonant element is proposed, namely its introduction instead of the integral element in the optimal transfer function according to the modulus criterion. The theoretical considerations are confirmed by simulation results.

Sliding coefficients estimation for fixed frequency sliding mode control of boost converter

The paper presents and analyses a control system for the Boost converter in which sliding mode control and classical PWM are combined into a fixed frequency sliding mode control system that emphasizes the advantages of both control methods. This leads to good responses of the power converter in dynamic and in steady-state regime, but a proper estimation of the control parameters is needed. Thus the fixed frequency sliding mode control is analyzed, the control function, the existence conditions and the stability conditions are calculated. Based on this calculations the conditions for the sliding mode coefficients are determined and interpreted for design purposes. Finally a algorithm for the estimation of sliding mode coefficients is proposed and the stated considerations are verified through simulation.

Performance analysis of slope and frequency modulated carrier PWM methods for grid connected converters

A detailed analysis of two Pulse-Width Modulation (PWM) methods is performed in this paper for grid connected converters. The considered methods are: sinusoidal carrier regulated by the slope of a trapezoidal waveform PWM (SLPWM) and frequency modulated triangular carrier PWM (HIPWM-FMTC). The analysis of the two PWM methods is realized with four performance indicators: standard and weighted total harmonic distortion (THD and WTHD), fulfillment of the grid connection requirements and minimum pulse width. The results are compared with those obtained for the Space Vector Modulation (SVPWM) and Selective Harmonic Elimination PWM (SHE-PWM). Experimental results are presented for a 1 kVA inverter prototype to validate the paper conclusions.

Design optimization methods of an intelligent controller from a speed control system

The paper presents fuzzy logic simple and combined with evolution strategies and neuro-fuzzy designs of a duty-cycle compensation controller in order to linearize the nonlinear external characteristics family of a step-down or forward DC-DC converter that supplies DC motors. The controller is additionally introduced in high precision speed control systems. Comparisons between classical PI controllers and fuzzy controllers are made. Advantages of combined methods of computational intelligence domain are revealed.

Automated system adjustment criterion for sinusoidal input signal

The paper presents a PWM control system of a sinusoidal voltage as output of a single-phase inverter with resistive load and LC low-pass filter. First the PWM control for a sinusoidal voltage and the control loop optimization via modulus criterion for step input signal are discussed, further analyzing the stationary error for a sinusoidal signal. This error can be reduced to zero by introducing a resonant element in the control loop. A new method of introducing a resonant element is proposed, such that the open loop transfer function of the system equals the transfer function derived from the modulus criterion multiplied by a resonant element and added by one or two compensating zeros. The presented method is confirmed by simulation results.